I\'m using Keycloak version 1.6.1, newly installed as a standalone application.
Keycloak should act as an IdP (Identity provider) for an SP (Service Provider) called Tab
Sometimes it's a good thing to specify in writing what you need - which I did here on Stack Overflow.
I found the URL to where on Keycloak one can export the IdP XML
https://keycloak-url/realms/{REALM-NAME}/protocol/saml/descriptor
That gave me the IDPSSODescriptor.
I'll leave this thread here, so people can benefit from my mistakes.